1. Field of the Invention
The present invention relates to the separation of a first gas, such as oxygen gas, from a mixed gas such as air containing oxygen and other selectably-adsorbable gaseous components.
The object is to provide a more efficient pressure swing adsorption (PSA) process for the production of a concentrated gas, such as oxygen, from a gas mixture, such as air, which process utilizes the adsorbent in a more efficient manner (lower bed size factor), and requires less energy than other processes using prior art technology to produce high purity gas from gas mixtures.
The PSA process is based upon the differential adsorption of selectively adsorbable gases and non-preferentially adsorbable gases, from mixtures thereof, on conventional adsorption bed materials such as zeolites. In the known process, the adsorption bed unit, or the first such bed unit of a two or three bed unit system, each of which may contain a lower bed stratum for removing water and carbon dioxide and an upper or downstream bed stratum for adsorbing the selectively adsorbable gas from supply of a gas mixture passed therethrough, is pressurized to a high pressure value to cause the selective removal of water and carbon dioxide and the selective adsorption of the one gas, while the pressurized non-selectively adsorbable gas is unaffected and passes through to a reception unit, which may be the second bed unit of the system. In such case the second bed unit becomes pressurized by the non-adsorbed gas, preparatory to coming on stream in the next cycle. The next bed unit, i.e. a third bed unit or the first bed unit of a two bed system, is being cleaned by back-flow or countercurrent evacuation by passing a supply of medium pressure waste gas or void gas purged from an equalization tank or from the bed unit being depressurized after producing the non-adsorbed, concentrated gas. This cleans the bed unit for subsequent repressurization and concentrated gas production. After a timed period the second bed unit is brought into sequential use, the first bed unit is evacuated and the second bed unit is repressurized.
Although many modifications and variations of the basic PSA cycle have been studied and applied to commercial processes, such as for the production of oxygen from air, such systems generally are inefficient and uneconomical for high purity production of oxygen for large plants when compared to the alternative method using cryogenic distillation. Therefore, it is an object of this invention to provide a highly efficient PSA process for producing large volumes of high purity oxygen from air with a lower power requirement.